1. Field of the Invention
The present invention relates generally to cartridge tape drives, and more particularly to adjusting the speed of tape to optimize operation of cartridge tape drives.
2. Description of the Prior Art
Magnetic tape storage devices are commonly used for the storage of large amounts of digital data because they provide an economical and reliable means for temporary and permanent storage. Because magnetic tape systems inherently rely on sequential recording, access times are substantially longer than other modern storage devices, but at the same time the danger of catastrophic failure is virtually absent. Thus it has become common practice to utilize tape systems as data backup for floppy disk and hard disk files, typically by reading out the entire contents of a random access memory system at the end of the day or other operating period, and retaining this data in storage until the next backup date or time. Where the volume of data is limited, one tape system and tape reel or cartridge may suffice, but where the data base is much larger, many reels or cartridges may be needed.
Tape drive systems have evolved over the past with technical improvements that have resulted in substantial increases in capacity accompanied by significant decreases in size. The cartridge (also called a cassette) used for these applications is very small, the standard cassette being 3.25" inches by 2.5" inches by 0.5" inches, with a nominal tape width of 0.25" inch. Both the data capacity and transfer rate for tape cartridges has increased over the years. For example, the Travan minicartridge, model TR-4, manufactured by Imation Corporation of St. Paul, Minn., has a data storage capacity of 4.0 gigabytes (GB)(uncompressed data) at a sustained transfer rate of 783 kilobytes-per-second (Kbps) when the tape is run at 120 inches per second (ips). Tape cartridges are expected to store 15 or more GB of uncompressed data in the near future.
Despite the technical improvements in tape drive systems including data cartridges, the data transfer rate is limited by the amount of heat which is generated by the cartridge when the tape is operated at its maximum speed of 120 ips. In particular, when the cartridge tape is operated at a relatively high speed for a period of time, such as at 120 ips for half an hour, a substantial amount of heat, due to friction between the components within the cartridge, is developed. After a period of time, such as when the cartridge is run at 120 ips for half an hour, the tape exceeds its safe operating temperature range. The heat must be dissipated to preclude malfunction of the cartridge tape and prevent degradation of the data being transferred.
In an attempt to overcome the above problem, the cartridge tape is commonly run at a slower speed than the specified maximum speed of 120 ips. In many cases, the tape is run at a speed of 90 ips or less. At this lower speed, overheating problems caused by the rubbing of individual components in the tape cartridge, such as the rollers, are minimized.
The obvious drawback to this approach, however, is that the data transfer rate of the tape is compromised. For example, to utilize a tape backup system efficiently, it is preferred to record the backup data at a high data transfer rate during what would normally be down time for the system, e.g. the time between the close of business one evening and the start of business the next morning.
What is needed therefore is an apparatus and method for minimizing the heat generated by the frictional components within the cartridge while optimizing the data transfer rate.